6" or 8"? Suck or blow??

[Blaze215]

What's up IC?
Quick question regarding air-cooled hoods. I would like to know what you guys thought is the best way to use your hoods. Should you suck air through them from the outside with the fan pulling in from the outside or should you have the fan outside pushing air through the hoods??

Another thing, what is your experience with the 8" hoods rather than the 6" hoods? I am planning on going with the Supersun 2 6" hoods but since I haven't purchased them yet there is still time to change.

Thanks,

215

 

[Phillthy]

sucking would be better in case there are any leaks in the hood. if you blow you would be blowing hot air out through those leaks. you would suck air through the the other way.

 

[Blaze215]

if you blow you would be blowing hot air out through those leaks

Thanks for the response Phillthy. If I were to blow then I would be blowing the cool air that is collected outside of the grow area through the hoods.


Does anyone else have a take on this?

 

[Guest]

pushing is more efficient fan wise,(make sure no air leaks) and hot air heating up the fan is not good as well ... the other way

 

[samba]

If you suck, you WILL have some smell with your exhaust, that is if your hoods leak
If your getting your air from outside, it wont matter if you suck or pull,it will be the same temp

And, go with 8" if you can!

 

[DrunkenMessiah]

pushing is more efficient fan wise,(make sure no air leaks) and hot air heating up the fan is not good as well ... the other way

Check your facts slips, pulling is ALWAYS more mechanically efficient. There are between 650 and 850 (the exact number is debated) muscles in your body. How many of them push? How about NONE of them!

Mechanically and aerodynamically you want to pull for as much of the distance as possible. Fans deal better with their pressure load when they can pull on it. You should always pull through restrictions in your air way such as carbon filters, elbows, size-reducers and so on. I have always pulled through vented hoods and cool tubes as well, but there is some merit to not doing this. Pulling the hot air over the fan motor certainly won't help its service life. Lately I have compromised. I use the fan to pull air out of the box and through the filter and then it pushes the non-stinky air through the cool tube or vented hood. This way you are pulling across most of your mechanical load whilst avoiding running the hot hood air over the motor. That said, all of the pro commercial guys pull through their vented hoods and they will daisy-chain a half-dozen of them onto a single fan. If you have enough effective air-flow (CFMs) the air coming off of the hoods isn't all that hot. Pull through a hood or cool-tube fast enough and the hot lamps don't have enough time to heat the air very much as it goes wooshing by.

If you suck, you WILL have some smell with your exhaust, that is if your hoods leak
If your getting your air from outside, it wont matter if you suck or pull,it will be the same temp

Samba here is just talking gibberish. Sucking is the only way to NOT get smell in your exaust. Pulling the air means that any leaks will be drawn through, not pushed out of. This means that one way or another, all of the air will make it through the filter. If you blow then even the TINIEST leaks will let stinky air out. Your setup has to be 100% PERFECTLY sealed for pushing to work, and even if you manage this it is still less efficient. As for his last sentance; sucking and pulling are the same thing, no idea what he's on about there.

Also, it is necessary to pull for stealth reasons. In order to keep smell from leaking your box needs to be at an effectively lower static pressure than the room that it is placed in (or if you grow in a whole room, the static pressure needs to be lower than that in your house). It doesn't take much, a couple of tenths of a millimeter of mercury worth of pressure difference is plenty. This makes it a necessity to pull the air from your box. If the box is at a higher pressure than the rest of the room then it becomes effectively impossible to keep the smell from leaking. As I said, you can push through your vented hoods while still pulling air from the box. This is a sort of best-of-both worlds when working with low-to-medium output fans. Once you get some serious airflow going however, the point becomes moot. If you are working with 400 CFM or more then just pull through the hoods as it will make a negliagable temperature difference for the fan motor. Good luck and happy gardening!

-DM

 

[John goodman]

Hi DM,

I got 3 x 600's in a line 5" inlet/outlet with only a little space between them...I.e carbon>fan>lamp>lamp>lamp> outside

I was hoping to pull thru the carbon then blow thru the 3 x 600, would you advise this? im happy to add another fan to the end of the chain...the fan attached to the carbon is 410cfm and Im will to add another as mentioned....any input greatly appreciated. The reflectors are sealed as best i can get them.

thanks in advance

 

[Bumble Buddy]

I consulted an expert, 8" reportedly is better, suck or blow don't matter apparently, "its all good"

 

[John goodman]

hahaha cheers ..I bet its all good lol

 

[Haps]

Actuallly, a blow job is mainly sucking, now where were we? Anybody ever have a chick try her first blow job and actually blow?
H

 

[Work2much]

He he, thats what I was thinking when I read the title.

 

[cork144]

if you running the cooled lights on a seperate line, its better to push with an 8" and maybe suck with a 6" at the end, then youll still have pos pressure making sure no odour leaks.

 

[DrunkenMessiah]

Hi DM,

I got 3 x 600's in a line 5" inlet/outlet with only a little space between them...I.e carbon>fan>lamp>lamp>lamp> outside

I was hoping to pull thru the carbon then blow thru the 3 x 600, would you advise this? im happy to add another fan to the end of the chain...the fan attached to the carbon is 410cfm and Im will to add another as mentioned....any input greatly appreciated. The reflectors are sealed as best i can get them.

thanks in advance

Sounds good to me, this is exactly like the compriamise I was talking about: pull through the filter and push over the lamps. Just make sure those hoods are sealed up nice and tight. Sounds like you've managed to minimize the distance that the fan is pushing which is what needs done to pull this off with a minimum of inefficiency. Adding an additional fan into the line at the very end would up the flow, but would then kindof defeat the purpose of that sortof configuration anyway. The whole point of doing it like this is to not draw heated air over the fan motor. See what you get running only the one fan, if the temps stay in check then just stick with that. Good luck and happy gardening!

-DM

*EDIT*

if you running the cooled lights on a seperate line, its better to push with an 8" and maybe suck with a 6" at the end, then youll still have pos pressure making sure no odour leaks.

Negative pressure is what prevents odor leaks bro, how on earth is positively pressurizing your stinky space going to help smell leaks? Positive pressure will push the smelly air OUT of any present leaks. If you run negative pressure then the system is going to draw clean air in through those same leaks and no smelly air makes it out. De-pressurize your grow space! This is the only sure-fire way to prevent smelly leakage.

 

[John goodman]

Thanks Dm..I'll give it a go and let ya know

 

[NorthernKronic]

Pull through the carbon filter and blow through the reflectors, this way if any air leaks it will leak out your reflector and back into the tent/grow or whatev..

If you pull through your reflector you run the risk of pulling stinky unfiltered air through any minute holes that might be there which can be stinky... but if you have a high quality reflector and you seal it well it shouldnt be a problem..

Personally though. I use one fan.. Pulling through the scrubber and blowing through the light.. No smell leakage here... Oh and I would go 8" if I were you.. Less restrictions, less noise.. more airflow..

But that brings us to the point that everyone should use 1 size up in ducting compared to their fan.. i.e. if you have a 6" fan use 8" ducting and so fourth.. Cuts down on noise and really improves the efficiency of your fan..

 

[DrunkenMessiah]

Lets say you have a 2 different fans. One is simply for the lights and the other is to provide fresh air for the plants. Obviously you'll want to have a carbon filter on the 'plant' exhaust fan but not on the 'light' exhaust. If you set it up so that the 'light' exhaust fan is sucking air through the reflectors, then any air leaks would contaminate the exhausted air. If you set it up where this fan BLOWS through the reflectors (positive pressure) than any leaks would be into the room and you would still have negative pressure because of the 'plant' exhaust fan. Its hard to explain, but its much better to do it this way if you are worried about leaks in the ducting and reflector.

Snap! Had no idea you where on about a dual-circuit design, guess I should have read more carefully. Yes, you are absolutely right on that one, if you are gonna run a whole separate unfiltered ventilation circuit to run a cool tube or vented hoods then pushing is the only way to go. Very good point for gardeners who run a dual circuit design (haven't seen one set up that way since back on the OG forums, it just didnt spring to mind when I read your post). Thanks for the clarification!